<html lang="zh-cmn-Hans">

<head>
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  <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
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  <title>Helloworld</title>
</head>

<body>

    <div class="row mb-3">
        <div class="col-6 bg-success">Helo1</div>
    </div>
    
    <div class="row mb-3">
        <div class="col-xl-12 col-lg-10 col-md-8 col-sm-4 col-6 bg-warning">Helo2</div>
    </div>
    
    <div class="row mb-3">
        <div class="col-12 col-md-6 bg-danger">Helo3a</div>
        <div class="col-12 col-md-6 bg-primary">Helo3b</div>
    </div>
    
    <div class="row">
        <div class="col-12 col-md-6 bg-danger">Helo4a</div>
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